Vector velocity system

ABSTRACT

Apparatus and method for measuring the angular velocity of an object in a single illumination utilizing a coherent system such as is utilized in a conventional doppler radar for radial velocity measurements. Apparatus and method for selecting specific frequency and bandwidth signals in the echo from the object illuminated by the coherent system, with the selected signal providing the data for subsequent computation to produce an output corresponding to the angular velocity of the object.

United States Patent [1 1 Constant 5] Mar. 19, 1974 VECTOR VELOCITYSYSTEM [76] Inventor: James Nickolas Constant, 1603 r Examlf'er Maynafiwllbur Danbury Dr Claremom Calm ASSISIG"! Examiner-6. E. ontone 9171 1Attorney, Agent, or Firm-Harris, Kern. Wallen &

T' l [22 Filed: Aug. 7, 1972 ey [21] Appl. No.: 278,536 [57] ABSTRACTRelated Application Data Apparatus and method for measuring the angularve- Continuation-impart 0f 27731 locity of an object in a singleillumination utilizing a 1970 abandonedcoherent system such as isutilized in a conventional doppler radar for radial velocitymeasurements. Appa- 52 us. Cl. 343/8, 343/9 mus and method for SelectingSpecific frequency and [51] 'l G015 9/44 bandwidth signals in the echofrom the object illumi- Fleld of Search 343/8, 9 mated y the coherentsystem with the Selected Signal providing the data for subsequentcomputation to pro- [56] References cued duce an output corresponding tothe angular velocity UNITED STATES PATENTS of the object. 2 6l7,09311/1952 Flyer 2348.713 8/1958 Cowart et a1. 343/8 25 Clam, 2 D'awmgFlgul'es LOCHL OSC/LL/QTOR F f l W fi/v m MN AM I l9 5 I I I than I I I67/ 0/ l! il Ml M! I I nu oo fin 10 {M0 5M0 I I I 26/ m m /x I IIND/C970)? l S VECTOR VELOCITY SYSTEM This invention is acontinuation-in-part of my copending application Ser. No. 27,731, nowabandoned, filed Apr. 13, 1970 entitled ANGLE DOPPLER SYS- TEM.

This invention relates to the determination of an objects vectorvelocity and more particularly to the determination of vector velocityin a single observation or illumination of the object using dopplerfrequency measurements. The vector velocity includes the angularvelocity and the path angle.

In many instances it is desirable to identify or measure directly thevector velocity of a particular object. Typical examples are in thefields of aircraft, vessel and vehicular control, etc. In these fields,it often happens that the object has an angular or nonradial velocityrelative to the observing site. Therefore, a suitable device, such asthe vector velocity system, must be provided to determine the objectsvector velocity. The vector velocity system permits the objects vectorvelocity to be determined in a single observation using conventionaltechniques.

An example of a system which is used to determine an objects radialvelocity is based on the well known doppler principle for its operationand is commonly referred to as doppler radar. In this conventionaldoppler radar, the radial velocity of the object is measured in a singleobservation. The angular velocity of the object may be obtained in aconventional doppler radar by making two or more successive timeobservations of the objects radial velocity as it moves in itstrajectory, noting the angle between the two directions of observation,and then usinga trigonometric solution to compute the angular velocity.In this case, the determination of the objects angular velocity isaccomplished indirectly through a series of individual observationsduring which the observing instrument is required to continually trackthe object over a portion of its trajectory and consequently at theexpense of tracking time.

The present invention is directed to a system which overcomes many ofthe problems and limitations encountered in the determination of angularvelocity present in the conventional doppler system. In accordance withthe present invention, a system can be designed to measure angularvelocity using conventional circuits or a doppler system can be modifiedto provide the added capability for angular velocity measurement aswell. The vector velocity system in accordance with the presentinvention uniquely provides the angular velocity measurement in a singleobservation or illumination of the object without recourse to the needfor continually trackingthe object and the related expenditure oftracking time, thus freeing the system for other target assignments.

Utilizing the system Of the present invention, data may be obtained froman object which will permit the determination of its vector velocity atany instant, i.e., in a single illumination of the object by the system.

It is therefore an objective of this invention to provide a system whichmeasures the vector velocity of an object relative to the observinginstrument at any instant. 4

A further objective of this invention is to provide a modificationcircuit for the conventional doppler system that will result inproviding the added capability for angular velocity measurements ofobjects moving relative to the observing instrument at any instant. Theterm at any instant is used to denote a single illumination of theobject by the radar or observing instrument. The term doppler is used todenote the determination of radial velocity from a measurement ofdoppler frequency shift by the signal. The term angle doppler is used todenote the determination of angular velocity from a measurement andsubsequent integration of a series of doppler frequency shifts by thesignal.

It is an object of the invention to provide apparatus and method formeasuring the angular velocity of an object in a single illuminationutilizing a coherent angle doppler system such as is utilized in aconventional doppler radar for radial velocity measurement. A furtherobject is to provide such apparatus and method which may be utilized inthe sonar and optical spectra as well as in the radar spectrum. Anadditional object is to provide apparatus and method for sorting out orselecting specific time varying signal frequencies in the echo from theobject illuminated by the coherent system, with the selected timevarying signal frequencies providing the data for subsequent processingusing conventional techniques to produce an output indication whichvaries as a function of the angular velocity of the object.

Other objects, advantages, features and results will more fully appearin the course of the following description. The drawing merely shows andthe description merely describes preferred embodiments of the presentinvention which are given by way of illustration or example.

In the drawings:

FIG. 1 is a block diagram of a velocity vector system incorporating thepresently preferred embodiment of the invention, and illustrating how adoppler system can be modified to provide the added capability forangular velocity measurement; and

FIG. 2 is a diagram illustrating the geometry of the vector velocitysystem.

The system of FIG. 1 includes a transmitter 10 operating at wavelengtha, a receiver 12, an antenna 13 of beam width angle 0, and a localoscillator 14 providing reference inputs for the transmitter andreceiver, to provide a coherent system. The system also includes a dataprocessor 17, and an indicator 18. The system may operate as a pulsed orcontinuous wave (CW) system. The system may operate with separateantennae for the transmitter and receiver or with a common antenna asdesired, and a common antenna arrangement is illustrated in FIG. 1. Thereceiver output includes a time varying signal of frequency f,,,,, andof bandwidth B produced by the echo from the object illuminated by andin transit of the antenna.

The data processor 17 includes a signal sorting unit 19 and a computer20. The signal sorting unit includes a plurality of signal selectioncircuits connected in parallel and identified as f,,,,, B where m 0,1,2,M and n 0,1 ,2,. N. The subscript m represents M-l-l possiblediscrete velocities V and the subscript n represents N+l possiblediscrete crossing angles (1). The total number of selection circuitsrequired is MXN, each circuit being determinative of a center frequencyf and bandwidth B where the double subscript designates the m forvelocity and n the crossing angle being measured by the circuit.

The individual signal selection circuits may be conventional in designand typically may be correlators,

matched filters and/or pulse compression filters. Each signal selectioncircuit has a center frequency f,, and frequency bandwidth B,,,,, wherethe center frequency increases as the value for the subscript nincreases. The number of circuits MXN and their frequencies f,, andbandwidths B,,,, have been determined in accordance with well knowndesign procedures to meet the particular application at hand. Thefrequency f,,,,, is the radar intermediate frequency (lF) for a givenangle of crossing while the frequency f is the highest doppler frequencywhich is expected to occur in the particular application. Not shown isthe similar circuit for negative frequencies, which is redundant in thepresent discussion.

The receiver output 25 is directly connected to each of the selectioncircuitsf B Any one of the vertical banks of circuits such as the bank fB f B indicated at 26, corresponds to a conventional doppler systemwhich provides the radial component of velocity of the objectilluminated by the beam from the transmitter antenna. Bandwidthidentification is not utilized in the conventional system. With theaddition of bandwidth identification and additional banks of circuitssuch as f B -f -B through f B -f B the system becomes the vectorvelocity system of the present invention with the output providing thevector velocity of the object illuminated by the beam from thetransmitter antenna. It should be recognized that in a conventionaldoppler system, the selection circuits are usually implemented as simplefrequency filters determinalive only of frequencies f,,,,,, whereas inthe system of the present invention, the selection circuits are usuallyimplemented as a bank of correlators, matched filters or pulsecompression filters determinative of both the doppler frequencies f,,,,,and the signal bandwidths B The computer may be a conventional computerwhich will perform the calculations to be described below. One input tothe computer is a signal from one of the selection circuits indicatingthe specific frequency f, and bandwidth B in the receiver output. Othercomputer inputs include system parameters of transmitter wavelength Aand antenna beam width angle 0. The range R from antenna to the objectmay also be in input, the range being determined by conventionaltechniques. The distance x between the source line of sight and theobject may also be computed, knowing the range and angular velocity.

The indicator 18 may be a conventional indicator such as an analog ordigital meter or a cathode ray tube or the like. Of course an indicatoris not essential and the computer output may be used directly forcontrol or additional computation without display when desired.

In operation, the signal which appears at the receiver output consistsof the transmitter frequency f,, and the doppler frequency f, the latterhaving frequency components corresponding to the radial and crossingvelocity components of objects illuminated by the antenna. Thetransmitter frequency f is located preferably in the intermediate bandportion of electromagnetic frequencies and is preferably fixed. The termintermediate is most frequently used to denote a frequency which islocated between the radio frequency (RF) and video frequency portions ofa radar system. The exact frequency used in any one case is determinedby the application at hand. Any of the well known types of intermediatefrequency receivers capable of producing oscillations at the neededfrequency f,, may be utilized. The vector velocity system just describedprovides vector velocity measurements of an object relative to a source.The term source is used here in referring to the transmitter and antennaor other radiator. While specific reference is made to the radarspectrum, the system is also applicable to the sonar and opticalspectra.

In order to describe the nature of the signal which results from themotion of an object relative to a source and the basis for thedetermination of its angular velocity using the vector velocity systemof the present invention, reference is made to FIG. 2. To facilitateannotation, the following description will be presented for a specificobject velocity V,,, and the subscript m will be omitted. Forconsideration of all velocities m 0,1,2,. ..M, the subscripts mn aresubstituted for the subscript n throughout equations l (5). Theinstantaneous frequency f which appears at the receiver output 25 isgiven to a close approximation by:

( l where f,, 2/ V x/R 2/)t V cos d) x/R n=0,l,2,...,N

)t. transmitted wavelength V velocity of the object in a directioninclined by the angle (1) d) angle between the direction of objectmotion and the normal to the radar line of sight V V radial and angularcomponents of the velocity V, respectively x distance between the objectand the line of sight R range between the object and the source Equation(2) is the doppler equation in the form which determines the radialcomponent V of the velocity V of an object while equation (3) is thedoppler equation in the form which determines the crossing or angularcomponent V of the velocity V. Equation (3) is called the angle dopplerequation to distinguish it from equation (2), the doppler equation. Theangle doppler equation is given in a variety of publications, forexample, in An Introduction to Synthetic Aperture Radar Brown andPorcello, IEEE Spectrum, September, 1969, p. 52 (see equation 8). Unlikethe doppler equation (2) wherein the radial component of the velocity Vis uniquely determined by the measurement of the doppler frequency f theangular component of the velocity V is not uniquely determined bymeasurement of the angle doppler frequency f,.' but also requires themeasurement or specification of the ratio x/R. If the instantaneousfrequencies are integrated in the manner of synthetic aperture radar,i.e., if a number of frequencies are taken, the integral of the ratiox/R is a known quantity, namely the angle 6 of the beamwidth from theantenna at 30. Integration therefore of the instantaneous frequenciesf,,' permits the unique determination of the angular component V of thevelocity V.

Equations (1), (2), and (3) indicate that the signal which appears atthe receiver output 25 consists of the sum of the steady and timevarying frequency components f and f respectively. Thus the signal at 25is a chirp or FM signal at the center frequency given by equation (2)and having a bandwidth determined by integrating equation (3), betweenthe limits for the angle 0,

In the system of the present invention, the chirp signal at 25 isprocessed in the data processor 17 of FIG. 1 in a manner which measuresbothf, and B,,, as example, by correlating the chirp signal with astored replica of itself. The correlation produces values for thefrequency f, and the bandwidth 3,, and therefore enables the computationof the radial and angular components of the velocity V using equations(2) and (4), respectively. In general, having measured the frequency f,and bandwidth B,,, the crossing angle 4),, may be computed by taking theratio of equations (2) and (4) and is given to a close approximation as:

5) Having the crossing angle the radial and angular components of thevelocity may be computed using equations (2) and (4). Sinceidentification of a specific f and B, for a selection circuit alsoidentifies a specific f,,', the offset distance x may be computed byequation In general, the object 32 moves in the direction between points34 and 35 with a velocity V. The line through points 34 and 35 and theline through points 31 and 32 which is normal to the radar line ofsight, defines the crossing angle d). Component velocities along theradial and angular directions relative to the source at 30 are given asV and V respectively. The distance between point 31 and object 32 is x.R,, is the shortest slant range between the source at 30 and thestraight line determined by points 31, 33 (with object 32 thereon). R isthe range between the source at 30 and the object at 32. R,,, is themaximum slant range (30 to 33) which is being illuminated by the source.The source at 30 has a beamwidth which defines the total angle of energywhich is being radiated by the source. The doppler frequencies whichoccur as a result of the radial velocity V and the angular velocity Vare given mathematically in small angle approximations by equations (2)and (3), respectively. The source is specified to be a coherent systemwhich includes a transmitter and antenna for illuminating objects, areceiver for measuring doppler frequencies, a data rocessor fordetermining the radial and angular velocity components of objects, andan indicator for displaying the information. In particular, the sourceis specified to have the capability for integrating and computing theinstantaneous signals f,,, given by equation (3), for the purpose ofdetermining the angular velocity V,,.

Thus it is seen that the coherent vector velocity system of theinvention includes a transmitter and receiver and an antenna forilluminating an object and provides for measuring the angular velocityof the object in a single observation or illumination. The systemincludes a data processor with selection circuits for sortingfrequencies contained in a chirp signal of predetermined frequency andbandwidth, with the output of the data processor being the computedvector velocity of the object. The receiver output is connected as aninput to the selection circuits and provides for each observation orillumination of the object an output signal of a specific frequency andbandwidth. Various of the conventional data processors may be utilized,including matched filters, correlators, and pulse compression filters,which may be implemented using well known hardware or computer softwaretechniques. The data processor provides for computation of the crossingangle, velocity components, and vector velocity of the object observedor illuminated by the antenna.

The vector velocity system of the present invention provides ameasurement of the angular velocity V, and the path angle d) with asingle observation or illumination of the object. Radial velocity V andrange R can be determined by conventional doppler techniques. Knowingangular velocity V and range R, the object offset distance x can becalculated by conventional techniques using equation (3).

Although the system of the present invention has been described in termsof adding the capability for measuring the angular or vector velocity ofobjects to a conventional doppler system, the system may be utilized toadd a similar capability to any type conventional system, for example toa synthetic aperture radar or to a sonar or to an optical or acousticsystem. All that is needed is for the system being modified to be acoherent system. It should be understood therefore that the scope of theinvention should not be limited by the particular embodiment of theinvention by way of description and illustration, but rather by theappendant claims.

I claim: 1. In a coherent vector velocity system having a transmitteroperating at wavelength A, a receiver and an antenna of beam width angle0 for illuminating an object, with the receiver output including the sumof steady in time and time varying frequency components produced by theecho from the illuminated object, the improvement for measuring theangular velocity of the object in a single illumination, including incombination:

a data processor having first sorting means and second computationmeans,

said first means including a plurality of selecting cir cuits connectedin parallel, each of said circuits selecting from the input thereto, asignal of a specific center frequency f,,,,, and a specific bandwidthB,,,,,, and providing an output signal identifying the circuit when aninput signal is selected,

said second means having the output signals of said selecting circuitsas an input and including means for computing the angular velocity V Aof the object illuminated for a specific selecting circuit outputsignal; and

circuit means for connecting the receiver output as an input to each ofsaid selecting circuits.

2. A system as defined in claim 1 wherein said means for computingangular velocity includes means for calculating B, (Z/MV 0.

3. A system as defined in claim 1 wherein said second means alsoincludes means for computing the angle d) of the path of the objectilluminated.

4. A system as defined in claim 3 wherein said means for computing pathangle includes means for calculating tan da =f /B 0.

5. A system as defined in claim 4 wherein said means for computingangular velocity includes means for calculating B,,.,. (2/)\)V 0.

6. A system as defined in claim 1 wherein said second means alsoincludes means for computing the radial velocity V of the objectilluminated.

7. A system as defined in claim 6 wherein said means for computingradial velocity includes means for calculating f, (2/A)V 8. A system asdefined in claim 6 wherein said second means also includes means forcomputing the vector velocity V of the object illuminated.

9. A system as defined in claim 1 wherein said second means alsoincludes means for computing the distance x between the object and theantenna line of sight.

10. A system as defined in claim 9 wherein said means for computingdistance it includes means for calculatingf Z/AV x/R, where R is thedistance between the object and the antenna, and f,,,,.' is the angledoppler frequency component of the receiver output.

11. A system as defined in claim 1 wherein said selecting circuitscomprise correlators.

12. A system as defined in claim 1 wherein said selecting circuitscomprise matched filters.

13. A system as defined in claim 1 wherein said selecting circuitscomprise pulse compression filters.

14. A system as defined in claim 1 wherein said transmitter operates asa pulsed transmitter.

15. A system as defined in claim 1 wherein said transmitter operates asa continuous wave (CW) transmitter.

16. A method of measuring the angular velocity V of an object in asingle illumination by a coherent vector velocity system having atransmitter operating at wavelength A, a receiver, and an antenna ofbeamwidth B,, produced by the echo from the illuminated object;

generating a selection signal corresponding to the specific frequencyand bandwidth in the receiver output; and

calculating the angular velocity V of the object for such specificfrequency and bandwidth.

117. The method of claim 16 including performing the calculation B(2/A)V '0.

18. The method of claim 16 including the step of calculating the pathangle (b of the object for such specific frequency and band width.

19. The method of claim 18 including performing the calculation tan rp=f,,,,,/B 0.

20. The method of claim 19 including performing the calculation B (Z/MV0.

21. The method of claim 16 including the step of calculating the radialvelocity V of the object illuminated.

22. The method of claim 21 including performing the calculation f,,,,,(Z/MV 23. The method of claim 2i including the step of ca]- culating thevector velocity V of the object illuminated.

24. The method of claim 16 including the step of calculating thedistance x between the object and the antenna line of sight.

25. The method of claim 24 including performing the calculation f,,,,,'Z/AV x/R, where R is the distance between the object and the antenna,and f,,,,, is the angle doppler frequency component of the receiveroutput.

1. In a coherent vector velocity system having a transmitter operatingat wavelength lambda , a receiver and an antenna of beam width angletheta for illuminating an object, with the receiver output including thesum of steady in time and time varying frequency components produced bythe echo from the illuminated object, the improvement for measuring theangular velocity of the object in a single illumination, including incombination: a data processor having first sorting means and secondcomputation means, said first means including a plurality of selectingcircuits connected in parallel, each of said circuits selecting from theinput thereto, a signal of a specific center frequency fmn and aspecific bandwidth Bmn, and providing an output signal identifying thecircuit when an input signal is selected, said second means having theoutput signals of said selecting circuits as an input and includingmeans for computing the angular velocity VA of the object illuminatedfor a specific selecting circuit output signal; and circuit means forconnecting the receiver output as an input to each of said selectingcircuits.
 2. A system as defined in claim 1 wherein said means forcomputing angular velocity includes means for calculating Bmn (2/ lambda)VA . theta .
 3. A system as defined in claim 1 wherein said secondmeans also includes means for computing the angle phi of the path of theobject illuminated.
 4. A system as defined in claim 3 wherein said meansfor computing path angle includes means for calculating tan phi mnfmn/Bmn . theta .
 5. A system as defined in claim 4 wherein said meansfor computing angular velocity includes means for calculating Bmn (2/lambda )VA . theta .
 6. A system as defined in claim 1 wherein saidsecond means also includes means for computing the radial velocity VR ofthe object illuminated.
 7. A system as defined in claim 6 wherein saidmeans for computing radial velocity includes means for calculating fmn(2/ lambda )VR.
 8. A system as defined in claim 6 wherein said secondmeans also includes means for computing the vector velocity V of theobject illuminated.
 9. A system as defined in claim 1 wherein saidsecond means also includes means for computing the distance x betweenthe object and the antenna line of sight.
 10. A system as defined inclaim 9 wherein said means for computing distance x includes means forcalculating fmn'' 2/ lambda VA . x/R, where R is the distance betweenthe object and the antenna, and fmn'' is the angle doppler frequencycomponent of the receiver output.
 11. A system as defined in claim 1wherein said selecting circuits comprise correlators.
 12. A system asdefined in claim 1 wherein said selecting circuits comprise matchedfilters.
 13. A system as defined in claim 1 wherein said selectingcircuits comprise pulse compression filters.
 14. A system as defined inclaim 1 wherein said transmitter operates as a pulsed transmitter.
 15. Asystem as defined in claim 1 wherein said transmitter operates as acontinuous wave (CW) transmitter.
 16. A method of measuring the angularvelocity VA of an object in a singLe illumination by a coherent vectorvelocity system having a transmitter operating at wavelength lambda , areceiver, and an antenna of beamwidth angle theta , including the stepsof: illuminating the object and receiving an echo from the object as itmoves along a path at angle phi and velocity V, with the receiver outputincluding a time varying signal of frequency fmn and bandwidth Bmnproduced by the echo from the illuminated object; generating a selectionsignal corresponding to the specific frequency and bandwidth in thereceiver output; and calculating the angular velocity VA of the objectfor such specific frequency and bandwidth.
 17. The method of claim 16including performing the calculation Bmn (2/ lambda )VA. theta .
 18. Themethod of claim 16 including the step of calculating the path angle phiof the object for such specific frequency and band width.
 19. The methodof claim 18 including performing the calculation tan phi mn fmn/Bmn .theta .
 20. The method of claim 19 including performing the calculationBmn (2/ lambda )VA . theta .
 21. The method of claim 16 including thestep of calculating the radial velocity VR of the object illuminated.22. The method of claim 21 including performing the calculation fmn (2/lambda )VR.
 23. The method of claim 21 including the step of calculatingthe vector velocity V of the object illuminated.
 24. The method of claim16 including the step of calculating the distance x between the objectand the antenna line of sight.
 25. The method of claim 24 includingperforming the calculation fmn'' 2/ lambda VA . x/R, where R is thedistance between the object and the antenna, and fmn'' is the angledoppler frequency component of the receiver output.